Insect or arthropod stings or bites are commonly occurring instances in human life, particularly in the rural areas. Stings or bites are usually caused by midges, biting flies, bees, wasps, such as yellow jacket and hornet, fire ants, spiders, etc. The stings or bites cause intense stinging, burning, pain, itching and tingling sensations. Clinically, these symptoms are referred to as hyperesthesia, paresthesia, dolor, and pruritus. Typically, after stung, the skin becomes red and swollen, and welting or pustule will form. Pustule is a small collection of pus in the top layer of skin (epidermis) or beneath it in the dermis. Pus is a mixture of inflammatory cells and liquid.
Currently, there is no effective medication for treating the intense stinging, burning, pain, itching and tingling sensations caused by the sting. It is typically recommended to immediately wash the stung area with soap and water, then cool off the skin with ice cubes or an ice-pack that has been wrapped in a cloth or thin towel, and rest the affected area and elevate it if possible to prevent excessive swelling. It is also recommended to use a painkilling cream or gel or an antihistamine to soothe the itch. However, the pain and burning sensations can be so intense, currently no topical medication stops the pain effectively. To the level of the pain reduction that the medicine can achieve, it will only last for a period of time because it merely numbs the affected area temporarily, but does not affect the cause of these symptoms.
On the other hand, skin contact with fireweed, stinging nettle, rhus plants or other noxious weeds or plants can also cause intense stinging, burning, pain, and itch, and frequently welting or pustules will form. Current treatments typically include topical application of an antihistamine, or cortisone cream to reduce the symptoms. Frequently, these are not effective to alleviate the symptoms caused by the noxious weeds or plants. The patients can suffer from severe discomfort for days after occurrence of the instance.
In the situation of either severe stings, or an extensive skin contact with noxious weeds or plants, frequently the patients have to go the emergency room for treatment.
The avermectin family of compounds is a series of very potent antiparasitic agents known to be useful against a broad spectrum of endoparasites and ectoparasites in mammals and also to have agricultural uses against various nematode and insect parasites found in and on crops and in soil. Ivermectin is a member of the avermectin family; it has been used as an antiparasitic agent to treat various animal parasites and parasitic diseases since mid-1980's. It is commercially available for animal use as Cardomec (for felines), Zimecterin (for equines) and Ivomec (for bovines) by MERIAL Limited, Duluth, Ga. The medicine is available in tablets, paste, or chewables for heartworm prevention, topical solution for ear mite treatment, or as oral or injectable solution for other parasite problems.
Ivermectin is also commercially available from Merck & Co., Inc for human use as Stromectol® for eradication of threadworm Strongyloides stercoralis, and for eradication of Onchocerca volvulus. The medicine is available in tablets and is orally administered by the patients.
Magda et al. Amer. J. Trop. Med. Hyg. 53(6) 1995 pp. 652-653 describe a method of topical application of ivermectin to treat head lice. Ivermectin is found to have a curative effect after a single topical application. U.S. Pat. No. 5,952,372 (to McDaniel) discloses a method of treating a form of rosacea associated with the ectoparasite Demodex by orally administering or topically applying ivermectin to fill and eliminate Demodex Follicuorum mites from hair follicles in affected skin.
U.S. Pat. Nos. 6,133,310, 6,433,006, 6,399,652, 6,399,651 and 6,319,945 (to Parks) disclose methods of treating acne rosacea, seborrheic dermatitis, acne vulgaris, transient acantholytic dermatitis, acne miliaris necrotica, acne varioliformis, perioral dermatitis, and acneiform eruptions by topically applying an avermectin compound, particularly ivermectin, to the affected areas.
None of the above described parasitic diseases and dermatological conditions are related to the hyperesthesia, paresthesia, dolor, and pruritus caused by insect or arthropod stings or bites, or skin contact with noxious weeds or plants. Insect or arthropod stings, or skin contact with noxious weeds or plants are common public problems. Therefore, there is a need for new and effective topical treatments for these conditions, particularly a treatment which can be applied immediately after the instance to reduce the suffering of a patient and to prevent further complications.